This invention relates in general to electronic brake control systems and in particular to a method for detecting a potential failure of wheel speed sensor wiring.
Many vehicles being currently produced by automotive manufacturers include electronic brake control systems that are integrated with their hydraulic brake systems. Such systems include anti-lock brake systems that prevent wheel lock-up during braking cycles, traction control systems to prevent slippage of driven wheels on low mu surfaces, rear brake boost systems that selectively increase the pressure applied to the vehicle rear wheel brakes and anti-roll control systems that provide roll over avoidance. Additionally, such systems also may assist in preventing loss of directional control when the vehicle is operated upon normal or even high mu surfaces, as can occur during accident avoidance maneuvers. All of the above functions may be incorporated as operating modes in a single electronic brake control system.
An electronic brake control system typically includes an electro-hydraulic control unit that is integrated with the brake lines of the hydraulic brake system. The electro-hydraulic control unit typically includes an Electronic Control Unit (ECU) that is mounted upon a hydraulic valve body. The ECU includes a microprocessor and control algorithm for operating the brake system. The algorithm and operating parameters for the vehicle are stored in a memory device that is electrically connected to the microprocessor. The memory device may be an integral part of the microprocessor or it may be separate therefrom. Additionally, the microprocessor is connected to and receives signals from vehicle operating parameter sensors, such as, for example, wheel speed sensors, vehicle motion sensors, a steering angle sensor and a throttle position sensor.
The hydraulic valve body includes a plurality of ports that are connected through hydraulic brake lines to components of the vehicle hydraulic brake system. A plurality of normally open and normally closed solenoid valves are disposed within the hydraulic valve body. The ECU is connected to the solenoid valve coils and operative to selectively actuate the valves. A pump also is typically mounted within the hydraulic valve body and is operative to supply pressurized brake fluid to the brake control system. The pump is controlled by the electronic control unit microprocessor.
During vehicle operation, the ECU microprocessor continuously receives signals from the various vehicle operating parameter sensors. When the microprocessor senses an impending vehicle control problem, the brake control system is activated. The microprocessor starts the pump to supply pressurized brake fluid and selectively actuates the solenoid valves to apply and relieve hydraulic pressure to the wheel brakes to correct the vehicle control problem.
Such electronic brake control systems typically include self-test algorithms to detect potential component failure. Among the components tested are the wheel speed sensors and the microprocessor in the ECU. These components are periodically tested to assure that they are properly functioning. Upon detecting a fault, the entire brake control system is disabled to assure safe operation of the vehicle and a warning, such the illumination of a lamp on the vehicle dashboard and/or sounding of an audio alarm, provided to the vehicle operator.